Method for continuous preparation of tobacco

ABSTRACT

A method for the continuous processing of tobacco to expand the tobacco, thereby reducing the tar and nicotine content of a given size cigarette, is disclosed. In carrying out the process, the tobacco preferably in shredded form, is moistened with water to a point at which its volume is approximately twice the initial volume, conveyed on a continuously moving conveyor into a freeze chamber and then into a freeze drying chamber wherein air at substantially atmospheric pressure and at about 30* F is passed over the tobacco shreds to effect drying. The drying is carried out to a point at which 90 percent of the moisture is removed. For moistening the tobacco initially, a technique employing floating the tobacco on water and subsequently lifting the tobacco therefrom by a screen may be employed. Further, the final drying may be accomplished in two stages utilizing two drying chambers.

I United States Patent [151 3,704,716

Abbott et al. [4 1 Dec. 5, 1972 METHOD FOR CONTINUOUS Primary Examiner-Melvin D. Rein PREPARATION OF TOBACCO Attorney-F. W. Anderson and C. E. Tripp [72} Inventors: John A. Abbott, Menlo Park; Clyde Donald Watson, San Jose, both of [57] ABSTRACT Calif- A method for the continuous processing of tobacco to [73] Assignee: FMC Corporation, San Jose, Calif. f i the tobacco F P re ducmg t and nicotine content of a given size cigarette, 1S disclosed. [22] Flledi 15, 1969 In carrying out the process, the tobacco preferably in [2]] Appl 884,850 shredded form, is moistenedwith water to a pointat Wl'llCh its volume 15 approximately twice the initial volume, conveyed on a continuously moving conveyor [52] U.S. Cl. ..13l/140 P, 131/136 i a freeze chamber and then i a freeze drying [5 l llll. Cl. ..A24b 03/18 chamber wherein air at substantially atmospheric pres Fleld of Search sure and at about 0 F is passed over the tobacco 131/17 34/5 99/199 shreds to effect drying. The drying is carried out to a 561 R f d point at which 90 percent of the moisture is removed. e erences For moistening the tobacco initially, a technique em- UNITED STATES PATENTS ploying floating the tobacco on water and subsequently lifting the tobacco therefrom by a screen 3,438,792 4/1969 Kruger ..99/199 may be employed Further, the fi l drying may be 2,596,183 5/1952 "131/140 complished in two stages utilizing two drying cham- 3,5l3,857 5/1970 Silvei'man ..l3l/l40 bers 3,245,l5l 4/1966 Eichmanns ..34/5

COLD AIR 10 Claims, 4 Drawing Figures HEATER BLOWER PATENTED DEC 5 I972 SHEET 1 OF 2 INVENTOR JOHN A.ABBOTT CLYDE DONALD WATSON BY W,

METHOD FOR CONTINUOUS PREPARATION OF TOBACCO BACKGROUND OF THE INVENTION There has recently been increased interest in the preparation of expanded tobacco for use in cigarettes. One reason for the interest lies in the increasing belief that some of the ingredients of cigarettes, such as'tar and nicotine, may be harmful to smokers. It has been recognized that expanded tobacco, by virtue of the expansion thereof, will contain a correspondingly diminished amount of deleterious ingredients when used in a cigarette of a given size. In other words, a cigarette containing expanded tobacco will contain less tobacco by weight, and hence less harmful ingredients, than a cigarette of the same size filled with unexpanded tobacco. Another recognized advantage for the producers of cigarettes of expanded tobacco is the reduction in the quantity of tobacco required to fill a given quantity of cigarettes.

It has been suggested that freeze drying of tobacco will produce'a desirable expanded tobacco suitable for cigarettes. However, the tobacco industry requires a huge continuous supply of tobacco which cannot be supplied with conventional freeze drying apparatus unless a tremendous capital investment is made in vacuum equipment for conventional freeze drying.

In conventional freeze drying, a frozen article is placed in a vacuum chamber wherein heat is supplied to the frozen article to cause the moisture in the article to pass from the solid state to the gaseous state without passing through a liquid state. Normally, because of the high vacuum required, freeze drying-is done by the limited volume batch process. Continuously supplying frozen tobacco to a vacuum chamber and continuously withdrawing tobacco therefrom would render it extremely expensive to maintain a sufficiently high vacuum in the chamber for the conventional freeze drying process.

SUMMARY OF THE INVENTION In the present invention, a continuous process, is provided for the preparation of fibrous material, such as tobacco for cigarettes. In one feature of the invention, frozen tobacco is continuously supplied to a drying chamber through which cool air is circulated at essentially atmospheric pressure. The moving air sweeps away the water vapor above the tobacco to reduce the pressure of the water vapor at the surface of the tobacco. In freeze drying, prompt removal of water vapor at the surface of the article is necessary for passage of the frozen moisture directly to the gaseous state, and a high vacuum, as used in conventional freeze drying, is useful to facilitate this transfer. But dry cool air blown past the article to sweep away water-vapor molecules as they reach the surface of the article can also be used, as described more fully in Science, Vol. 130, l 1 Sept. I959, pages 628-629, and in Meat, July and Aug. 1963, pages 34 and 26, respectively. Frozen shredded tobacco, which has a high freezing point and a relatively large surface area per unit of mass is especially well suited to this type of drying.

In the present invention, frozen tobacco is moved continuously while being frozen, as through a freezing 0 about a percent to 13 percent moisture content) and chamber, and while being freeze dried, as through a drying chamber through which cool air is circulated at in the form of shrunken shreds. The tobacco is first moistenedfor expansion, either by passing the tobacco under a water spray or floating the tobacco in a body of water. In the latter instance, a wire mesh conveyor passes through the surface of the water to raise and drain the water soaked tobacco. When the expanded tobacco is subsequently freeze dried as described above, the tobacco 'will remain in the expanded condition even after drying.

. The tobacco is fed preferably by a continuously moving belt from a'source of supply through the wetting step to a succession of separate chambers, in each of which a separate treatment is performed on the tobacco, so that fully processed tobacco is continuously delivered from the final downstream chamber.

It is therefore one object of the present invention to provide a method and apparatus for the continuous freeze drying of shredded fibrous material to produce an expanded material.

It is another object of the present invention to provide for continuous freeze drying of tobacco at atmospheric pressure. I

It is yet another object of the present invention to continuously soak tobacco and raise the tobacco for transfer into a freezer.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and 1B are side views, in cross section, of apparatus constructed in accordance with one form of the invention for preparing tobacco for use in cigarettes, showing schematically one form of apparatus for'supplying air of the desired temperature and relative humidity to one of the chambers.

FIG. 2 is a fragmentary plan view of the apparatus of FIG. 1; and

FIG. 3 is a side view, in cross-section, of apparatus constructed according to one feature of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT There is shown in FIGS. 1A and 1B apparatus for continuously expanding tobacco for use in cigarettes. A conveyor 8, mounted on conveyor frame 9 (FIG. 2) has an endless wire mesh conveyor belt 10, with a horizontal upper run 11. Tobacco Tl, which is shredded (to, say, 50 cuts per inch) and dry (say 10 percent to 13 percent moisture) is continuously deposited on the downstream end of the conveyor from a supply conveyor 12. A plurality of sprinkler manifolds 13 above the upper run 11 of the belt extend across the conveyor to continuously discharge water on the belt 10, the tobacco T1 falling onto the belt, and the tobacco in the belt. On wetting, the tobacco expands typically 2.6 times and contains percent to percent moisture. The wet, expanded, tobacco is designated as T2.

The conveyor 8 extends through inlet and outlet openings 14a, 14b of an enclosed insulated freezing chamber 14 through which cold air, at about F, is circulated tov freeze the wet tobacco which is continuously moving through the chamber 14 on the belt '10. The frozen tobacco is indicated as T3. 7

From the chamber 14, the conveyor 8. extends through inlet and outlet openings 15a, 15b of an insulated drying chamber 15. The chamber 15, which is enclosed, has an air inlet opening 16 in communication with an inlet duct 17 and has an outlet opening 18 in communication with art outlet duct 19. As shown schematically in FIG. 1A, air is drawn from chamber 15 and through duct 19 by a blower 20 connected to the duct 19. The'blower 20'discharges air through a cooling chamber 21 where the air iscooled to typically 20 by a refrigerator unit 22. Moisture is condensed out of the air in the cooling chamber and when the air, which is carried through heater '23 to inlet duct 17', is sub sequently heated in the heater to about 30, the air becomes very dry. The dry air from heater 23 passes into the inlet duct 17 for circulation through chamber 15. The final temperature of the air introduced to the chamber 15 can be regulated by the adjustable knob-24 on'theelectric power supply 25 which transmits electrical energy to the heating elements 26. Another method of supplying dry air would be to circulate the air through a bed of solid particulate dessicant, such as silica gel or materials known commercially as molecular sieves. Thus, dry (relative humidity less that 10 percent and cool air (about F) is continuously circulated through the chamber 15. Although air at the temperature and relative humidity indicated is preferred, it is only necessary that the air have a temperature and humidity so that the wet bulb temperature thereof is below the freezing point of the water soaked tobacco.

The dry cool air circulating through chamber 15 penetrates the frozen tobacco T3 and sweeps away the water molecules from the surface of the shredded tobacco, which has a relatively large surface area. The rate of release of the water vapor from the frozen tobacco T3 is controlled primarily by the water vapor pressure at the surface of the tobacco rather than by total gas pressure. Although in conventional freeze drying, a vacuum is used to reduce the water-vapor pressure at the surface of the article being freeze-dried, the circulating dry, cool air will also effectively reduce the water-vapor pressure at the surface of material, such as the fibrous shredded tobacco. Thus, as in conventional freeze drying, the water vapor in the shredded tobacco will pass directly to gaseous vapor without passing through the liquid stage. This sublimation of the vapor in the tobacco will completely dry the tobacco, without shrinking the tobacco from the expanded state, if the continuously moving tobacco is exposed for a sufficiently long time to the cool dry air of the drying chamber 15, which, for convenience, may be referred to as a first drying chamber. If the tobacco is exposed for a lesser time to the air circulating through chamber 15, the tobacco will be only partially dried. The partially dried tobacco is indicated at T4.

In order to save time in the drying cycle, a second insulated drying chamber 30 may be provided, directly downstream (with respect to the direction of tobacco travel on the conveyor 8) from the first drying chamber 15. The conveyor 8 extends through inlet and outlet openings 30a, 30b in the chamber 30 and carries the tobacco through thatchamber for completion of the drying. The drying is completed quickly by the circulation of warm (say l00 F), dry (say 10 percent relative humidity) air through the chamber. Although air'at the temperature and humidity indicated is preferred, it .is only necessary that the air beata temperature and humidity so that the wet bulb temperature thereof is above the freezing point of the partially freeze dried tobacco. The completely dried tobacco is indicated at T5. As the remaining vapor in the tobacco dries in chamber 30, the vapor passes through the liquid stage before finally evaporating. For this reason, it ispreferable to freeze dry at least 90 percent of the moisture from the tobacco in chamber 15 so that there will not be a significant shrinkage of the tobacco when the remaining vapor passes through the liquid stage in chamber 30. I v d After the final drying, the tobacco is completely dry and brittle, although remaining in the expanded state of over twice the size'of the original tobacco T1. In order tofacilitate further handling, the tobacco moves on conveyor 8 through inlet opening and outlet opening 31a, 31b of an insulated rehumidifying chamber 3]. Warm moist air (of, for example, 80 percent relative humidity and 80F) is circulated through the chamber to add moisture, say 10 percent to 13 percent to the dry tobacco. The rehumidified tobacco is'indicated at T6.

The tobacco thus is carried by the wire mesh conveyor successively and continuously through a wetting operation, and insulated chambers 14, 15, 30, 31 for separate treatment in each of the chambers while the tobacco is moved through the chambers. The tobacco in its processed form is continuously discharged through opening 31b of the final downstream chamber In lieu of wetting the tobacco by sprinkling, the tobacco Tl may, instead, be dropped into a tank 40 from the supply conveyor 12. The tank 40 is filled with water which soaks the tobacco to a moisture content of 70 to 90 percent. The downstream end of a conveyor 41 has a drum 42 mounted in the tank 40 below the surface of the water; An endless wire mesh conveyor belt 42, having an upper run 43 and a lower run 44, is received over drum 42. The wire mesh conveyor belt, which defines a continuous screen, has small closely spaced openings through which excess water drains. Two vertically spaced drums 45, 46 are positioned above the tank at the downstream end thereof. The upper run 43 of the conveyor belt is received over the upper drum 45 and the lower run 44 of the conveyor belt is received over the lower drum 46. The upper run 43 of the conveyor belt extends through a series of chambers similar to the construction shown in FIGS. 1A and 1B.

As a continuous supply of tobacco T1 drops off the end of supply conveyor 12, it floats on the water in the tank. The continuous supply of tobacco spreads across the water until the floating, soaked, tobacco contacts the wire mesh conveyor run 43 as it emerges through the surface of the water. The wetted tobacco T2 is then picked up and carried through the processing steps previously described in conjunction with FIGS. 1A and 1B.

Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention.

What is claimed is:

l. A method of processing shrunken shredded tobacco to effect expansion thereof comprising the steps of moistening the tobacco having an initial moisture of about percent with water to swell the shredded fibrous particles thereof, to about twice the initial volume and having about 70 percent to 80 percent moisture continuously moving the swollen fibers to a freeze chamber wherein cold air at about 32F. or lower is passed over the fibers to effect freezing, continuously moving the fibers from the freeze chamber to a drying chamber, and passing cool dry air at atmospheric pressure through the drying chamber to freeze dry the frozen fibers to a point where approximately 90 percent of the moisture is removed therefrom while the tobacco maintains substantially its expanded volume as they move through the drying chamber wherein the wet bulb temperature of the cool dry air is below the freezing point of the water soaked tobacco, said processing steps being effected as said tobacco is transported by conveying elements.

2. A method according to claim 1 wherein said air at atmospheric pressure is at a temperature of about 30 F. with a relative humidity ofless that 10 percent.

3. A method according to claim 4 wherein said air at atmospheric pressure is at a temperature of about 30 F. with a relative humidity of less than 10 percent.

4. A method of processing shrunken shredded tobacco comprising the steps of wetting the material with water to swell the shredded fibrous particles thereof, continuously moving the swollen fibers to a freeze chamber for freezing, continuously moving the frozen fibers from the freeze chamber to a first drying chamber, passing air at atmospheric pressure and a cool temperature through the first drying chamber to freeze dry the frozen fibers to a point where approximately 90 percent of the moisture is removed therefrom as they move continuously through the first drying chamber with the wet bulb temperature of said cool air being below the freezing point of the water soaked tobacco, continuously moving the partially freeze dried fibrous particles from the first drying chamber to a second drying chamber, and passing air which is substantially warmer than said cool air through the second drying chamber to further dry the tobacco particles.

5. The method of claim 4 followed by the step of continuously moving the dried tobacco particles into a rehumidification chamber and passing moist air through the rehumidification chamber.

6. In a process for preparing tobacco, the steps of distributing an even floating layer of tobacco shreds on a body of water to swell them, lifting a screen through the water surface to raise the tobacco shreds from the water and to drain the water from the shreds through the screen, freezing the soaked shreds on the screen, and freeze drying the tobacco shreds while they remain on said screen by passing air through the tobacco and screen.

7. In a process for preparing tobacco, the steps ofdisbulb temperature is below the freezing point of the water soaked tobacco, and finish drying the tobacco while it remains on the screen by passing air through the tobacco and screen with the air at a temperature and relative humidity such that its wet bulb temperature is above the freezing point of the partially freeze dried tobacco.

8. The method of claim 7 followed by the step of moisture conditioning the tobacco by passing a warm current of moist air past the tobacco as it remains on said screen.

9. In a process according to claim 7 wherein said screen is continuously moved so that the tobacco progresses continuously from said body of water to the point where it is finish dried.

10. In a process according to claim 7 wherein approximately percent of the moisture is removed from the tobacco during the partial freeze drying portion of the process. 

1. A method of processing shrunken shredded tobacco to effect expansion thereof comprising the steps of moistening the tobacco having an initial moisture of about 10 percent with water to swell the shredded fibrous particles thereof, to about twice the initial volume and having about 70 percent to 80 percent moisture continuously moving the swollen fibers to a freeze chamber wherein cold air at about 32*F. or lower is passed over the fibers to effect freezing, continuously moving the fibers from the freeze chamber to a drying chamber, and passing cool dry air at atmospheric pressure through the drying chamber to freeze dry the frozen fibers to a point where approximately 90 percent of the moisture is removed therefrom while the tobacco maintains substantially its expanded volume as they move through the drying chamber wherein the wet bulb temperature of the cool dry air is below the freezing point of the water soaked tobacco, said proceSsing steps being effected as said tobacco is transported by conveying elements.
 2. A method according to claim 1 wherein said air at atmospheric pressure is at a temperature of about 30* F. with a relative humidity of less that 10 percent.
 3. A method according to claim 4 wherein said air at atmospheric pressure is at a temperature of about 30* F. with a relative humidity of less than 10 percent.
 4. A method of processing shrunken shredded tobacco comprising the steps of wetting the material with water to swell the shredded fibrous particles thereof, continuously moving the swollen fibers to a freeze chamber for freezing, continuously moving the frozen fibers from the freeze chamber to a first drying chamber, passing air at atmospheric pressure and a cool temperature through the first drying chamber to freeze dry the frozen fibers to a point where approximately 90 percent of the moisture is removed therefrom as they move continuously through the first drying chamber with the wet bulb temperature of said cool air being below the freezing point of the water soaked tobacco, continuously moving the partially freeze dried fibrous particles from the first drying chamber to a second drying chamber, and passing air which is substantially warmer than said cool air through the second drying chamber to further dry the tobacco particles.
 5. The method of claim 4 followed by the step of continuously moving the dried tobacco particles into a rehumidification chamber and passing moist air through the rehumidification chamber.
 6. In a process for preparing tobacco, the steps of distributing an even floating layer of tobacco shreds on a body of water to swell them, lifting a screen through the water surface to raise the tobacco shreds from the water and to drain the water from the shreds through the screen, freezing the soaked shreds on the screen, and freeze drying the tobacco shreds while they remain on said screen by passing air through the tobacco and screen.
 7. In a process for preparing tobacco, the steps of distributing an even floating layer of tobacco shreds on a body of water to swell them, lifting a screen through the water surface to raise the tobacco shreds from the water and to drain the water from the shreds through the screen, freezing the soaked shreds on the screen, partially freeze drying the shreds by passing an air stream by the shreds and through the screen as the shreds remain on the screen, the air stream having a relative humidity and temperature such that its wet bulb temperature is below the freezing point of the water soaked tobacco, and finish drying the tobacco while it remains on the screen by passing air through the tobacco and screen with the air at a temperature and relative humidity such that its wet bulb temperature is above the freezing point of the partially freeze dried tobacco.
 8. The method of claim 7 followed by the step of moisture conditioning the tobacco by passing a warm current of moist air past the tobacco as it remains on said screen.
 9. In a process according to claim 7 wherein said screen is continuously moved so that the tobacco progresses continuously from said body of water to the point where it is finish dried.
 10. In a process according to claim 7 wherein approximately 90 percent of the moisture is removed from the tobacco during the partial freeze drying portion of the process. 